An industrial robot includes a manipulator and a control unit having means for automatically operating the manipulator. There are different types of manipulators, such as a serial kinematic manipulator and a parallel kinematic manipulator. Today fast handling and assembly of components on a flat surface, such as the surface of a conveyor is typically performed by parallel kinematic manipulators.
A parallel kinematic manipulator (PKM) is defined as a manipulator comprising at least one stationary element, a movable element, denoted a platform, and usually three arms. Each arm comprises a link arrangement connected to the movable platform. Each arm is actuated by an actuator preferably arranged on the stationary element to reduce the moving mass. The link arrangements transfer forces to the movable platform. For a fully built-up parallel kinematic manipulator for movement of the platform with three degrees of freedom, three parallel-working arms are required. To obtain a stiff arm system with a large loading capacity and a low weight, the arms connected to the movable platform of the parallel kinematic manipulator should have a total of six links.
There exist different types of manipulators for fast material handling, pick and place, and assembly, such as the Scara manipulator, the Gantry manipulator, and the Delta PKM manipulator. The Delta PKM manipulators are taking market shares from especially the Scara manipulators, because of its lightweight arm structure, which provides higher dynamic performance in relation to manipulator manufacturing cost. However, the Scara manipulator has some features that cannot be achieved by the Delta manipulator, as for example small footprint, possibility to mount the manipulator beside the work space, possibilities to obtain a larger vertical stroke and the possibilities to make installations with a higher manipulator density. Looking at the kinematics, increasing the horizontal work space size means only that the arms of the Scara manipulator need to be resized while for the Delta manipulator the whole framework and the manipulator must be resized, which means that the manipulator will need to be located higher above the work space.
In order to combine the advantages of the traditional Scara kinematics with the performance potential of the Delta PKM manipulator, a Scara Tau PKM concept was developed. This concept is disclosed in WO 03/066289. The prior art Scara Tau manipulator has three inner arm parts mounted on three bearings, which are in turn mounted on a vertical column, which also holds the motors with its gear boxes. The output shaft from the gear box is connected to a gear wheel, which engages a gear ring mounted on the arm side of the arm bearing. Because the motor and gear box must be mounted with their shafts parallel with the rotation axes of the arms, a lot of space is needed between the arm bearings in order to get the space needed for the actuation system. This means that even if the robot obtains a small footprint it will need a lot of space in the vertical direction. This is especially a problem if the robot is used to serve for example a conveyor, especially if the robot must be mounted over the conveyor. Beside the need of a large space in the z-direction, the prior art robot will also be heavy because of the mounting column supporting the arms and the actuation system.